Power brake problem...need to know what to check - Team Camaro Tech
Brakes, Suspension & Steering Conversion questions, Steering & Handling

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post #1 of 26 (permalink) Old Feb 14th, 09, 07:59 PM Thread Starter
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Dan
 
Join Date: Feb 2007
Location: Summerfield, NC
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Power brake problem...need to know what to check

Recap: Car has power brakes, but they've always felt like manual brakes. No power assist at all.

Today I replaced the booster. Just started up the car and pushed in the pedal. No change in the feel...pedal still hard as a rock.

Please tell me things I need to check that could cause no boost assist at all. I don't want to keep throwing money at parts that don't solve the problem.

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #2 of 26 (permalink) Old Feb 14th, 09, 08:15 PM
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bill
 
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Re: Power brake problem...need to know what to check

did you check for vacumn at brake booster.it needs vacumn to work right.
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post #3 of 26 (permalink) Old Feb 14th, 09, 08:25 PM Thread Starter
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Dan
 
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Re: Power brake problem...need to know what to check

Yes...forgot to mention that. The engine is pulling vac. With the last booster, after I ran the car, then shut it down, when I pulled out the check valve, you could hear air rushing back into the booster.

I think I have 14" of vac. A friend measured it for me a while ago.

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #4 of 26 (permalink) Old Feb 14th, 09, 11:00 PM
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Philip
 
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Re: Power brake problem...need to know what to check

The booster needs to be able to vent the air inand out of the atmospheric side to work.
That vent on the side of the booster where the pedal rod is. If this is covered by the firewall insulation (or anything else) the booster will not work properly.


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post #5 of 26 (permalink) Old Feb 15th, 09, 06:40 AM Thread Starter
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Dan
 
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Re: Power brake problem...need to know what to check

I don't have any insulation on the firewall. Where exactly is the vent on the backside? I don't remember seeing anything.


Couple more questions:

inside the car...how far from the firewall should the bracket attach to the pedal?

Anyone have a good picture of the inside of the car where the booster pushrod comes out so I can compare the angles?

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #6 of 26 (permalink) Old Feb 15th, 09, 06:08 PM Thread Starter
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Dan
 
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Re: Power brake problem...need to know what to check

Here's a couple pictures I just too. See any problems with anything here?


Here's the goodies in the engine bay. Booster & check valve are brand spanking new.


Does that look like a power brake M/C? I forget to measure the bore while I had the damn thing off.


Here's view from under the dash.


Here's the rear of the Carb from the Driver Side. You can see the vac hose here.


and the Passenger Side.

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #7 of 26 (permalink) Old Feb 15th, 09, 06:17 PM
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Robert
 
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Re: Power brake problem...need to know what to check

I can't tell from your pic's but if you have the booster vac line tee'd with the PCV it will do exactly as you described.
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post #8 of 26 (permalink) Old Feb 15th, 09, 06:22 PM Thread Starter
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Dan
 
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Re: Power brake problem...need to know what to check

In the bottom picture, the Booster is on the left and the PCV is on the right. They are each in their own port. If that's not right, where else would I put the PCV?

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #9 of 26 (permalink) Old Feb 15th, 09, 06:24 PM
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Mike
 
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Re: Power brake problem...need to know what to check

There are 2 holes on the brake pedal for the booster to hook to. With a booster is goes on the bottom hole. Manual brakes go in the top hole.

Did the brakes ever work good? Were they manual before and you change to power brakes? It would be good to know the bore size of the master cylinder.

I had too big a bore in my master cylinder and the car would run thru the brakes. The pedal did go down some so the booster was working. I went to a smaller bore master and it fixed my problem.

I had a 1" bore master cylinder and went to a 15/16" bore and just that 1/16" made a difference.

Smaller bore more pressure.
Bigger bore less pressure.

Mike
69 Camaro Prostreet - purple w/ghost flames , 502 w/ 871 blower


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post #10 of 26 (permalink) Old Feb 15th, 09, 06:45 PM Thread Starter
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Dan
 
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Re: Power brake problem...need to know what to check

The car had manual brakes when I bought it. The shop I bought it from converted them to power brakes. Does the picture of the pedal looks right? I only see one hole in the pedal.

I thought the reason for the lower mounting hole was so the power brakes wouldn't be so twitchy.


The brakes never worked like they should.

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #11 of 26 (permalink) Old Feb 15th, 09, 08:50 PM
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Robert
 
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Re: Power brake problem...need to know what to check

The lower hole gives the correct "ratio" for power brakes. Nothing really to do with "hard pedal".
Disconnect the PCV, plug the source and see if the brakes improve.
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post #12 of 26 (permalink) Old Feb 16th, 09, 09:18 AM
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Re: Power brake problem...need to know what to check

It looks to me that its the master from manual brakes. I know there are different ones out there but I dont see the second line to the fronts from the valve. The 70s style valve is quite common in the conversion kits, that is not it. If its the original style isnt there a residual valve as well for the rears? Try jacking it up and have someone lightly touch the brakes see if all are working. It could even be the rear hose over the axle.
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post #13 of 26 (permalink) Old Feb 16th, 09, 12:41 PM
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Ron
 
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Re: Power brake problem...need to know what to check

I would think you need to drill a hole about 1" below the existing hole on the brake pedal arm and readjust (back off threads) and install the brake pedal pushrod on new (lower) hole.....Usually the brake pedal arm has these 2 holes from the factory (top hole-manual brakes, bottom hole-power brakes).....At least try backing off the threaded rod as this could be binding the diaphragm in the power brake booster causing your "hard brake" problem!
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post #14 of 26 (permalink) Old Feb 16th, 09, 01:13 PM Thread Starter
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Dan
 
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Re: Power brake problem...need to know what to check

I've got the braket almost to the end of the threaded rod. If the pushrod was binding in the diaphram, wouldn't that make the car not stop at all?

I can push the pedal and the car will stop...just don't have any boost. Does this really sound like a binding pushrod? Anyway to test for this?

I did have to push the braket up a bit to get it into the hole on the brake pedeal. I wouldn't say I had to force it up...just had to go up a bit. Is that a problem?

Dan

1968 RS - Black
408 w/ Muncie 4 speed & 12 bolt rear
Deluxe Houndstooth Interior
Dropped 2" with TeamIII Mini-Lites

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post #15 of 26 (permalink) Old Feb 16th, 09, 03:09 PM
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Dan
 
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Re: Power brake problem...need to know what to check

DB, you should baseline your brakes to the AIM to make sure you have the correct pedal, also check all your measurements: pedal to floor, booster pushrod to M/C sounds like you may have mismatched parts, your booster pushrod should align right up to the lower hole like everyone mentions on the pedal It shouldnt have any pressure on it up or down when in the detent position also your pedal should have a little play prior to any brake engagement, did your new booster come with a mounting bracket? check the AIM and dpozzis site for more inf. Dan in Ft. Lauderdale

68 camaro RS 327/275 THM350 4 wheel disc brake 8.5 10 bolt 3.42 daily driver
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